The American feminist who half a century ago fought a campaign to popularise the honorific “Ms” for women, which is now in mainstream use, has died aged 78.

Though Sheila Michaels did not invent the term, she turned it into a symbol signifying a woman’s right not to be defined by any relationships to men.

She began her campaign in 1961, but it would be 10 years before “Ms” was adopted as the title of a feminist magazine, and 25 years before it appeared on the front page of the New York Times.

Michaels had first seen “Ms” on an address label on a Marxist magazine posted to a Manhattan housemate and initially thought it was a typo.

It resonated with her, both as a feminist, and also as a child of unmarried parents, she told the New York Times in an interview last year for her own obituary.

She was looking for a title for a woman who did not “belong” to a man, she told the Guardian in 2007.

“There was no place for me. No one wanted to claim me and I didn’t want to be owned. I didn’t belong to my father and I didn’t want to belong to my husband – someone who could tell me what to do. I had not seen very many marriages I’d want to emulate – the whole idea came to me in a couple of hours. Tops,” she said.

She later recalled thinking of the significance on first seeing that address label. “Wonderful,” she told the Japan Times, an English-language newspaper in 2000. “‘Ms’ is me!”

Michaels, a feminist and civil rights campaigner, who worked mostly as a writer, editor and publicist, began what she would later describe as a “timid eight-year crusade”.

When she found herself, in 1969, invited to the popular liberal New York FM radio station WBAI, she introduced the term, provoking a discussion that reached the ears of Gloria Steinem, who was looking for a name for the women’s magazine she was founding.

Ms magazine appeared in 1972, with its first issue selling out in eight days. Shortly afterwards, a New York congresswoman introduced legislation that said women did not have to disclose their marital status on federal forms.

In 1986, the honorific was adopted by the New York Times, appearing on the front page. An editor’s note read: “Until now ‘Ms’ had not been used because of the belief that it had not passed sufficiently into the language to be accepted as common usage. The Times now believe that ‘Ms’ has become part of the language and is changing its policy.”

The term Ms dates back to at least 1901 and was originally a shortened form for Mistress.

“Apparently it was in use in stenographic books for a while,” Michaels told the New York Times. “I had never seen it before. It was kind of arcane knowledge.”

When she first introduced it into that feminist radio discussion and was asked how to pronounce it, she said: “I answered, ‘Miz’.”

She traced the pronunciation back to her mid-Southern roots. “Growing up in St Louis, Missouri, I’d developed a curiosity about a woman known as Miz Noble who lived behind our house. I wondered whether this meant she was unmarried or a widow. I liked the ambiguity,” she once said.

In 1961, women tended to marry younger. Being a “Miss” implied you had been left on the shelf, she believed, and employers wanted to know marital status. Michaels said: “The first thing anyone wanted to know about you was whether you were married yet. I’d be damned if I’d bow to them.”

Michaels, who lived in Manhattan, married the chef Hikaru Shiki, with whom she ran a Japanese restaurant in Lower Manhattan in the 1980s. They were later divorced.